Heavenly Onion Casserole

This onion casserole is basically French onion soup in casserole form. Sweet Vidalia onions and mushrooms sauteed in butter, layered with Swiss cheese, and baked under slices of French bread that soak up a creamy mushroom soup sauce.

The four-hour refrigeration isn’t just for convenience. That resting time lets the bread absorb the soup and evaporated milk mixture, so when it bakes, the bread layer turns into something between a savory bread pudding and a gratin crust. Skip the chill and the bread sits on top like dry toast.

Uncover the casserole for the last 20 minutes to let the Swiss cheese slices on top melt and turn golden brown. That bronzed, bubbly cheese layer is what earns this dish the “heavenly” title.

Pro Tips

• Use Vidalia or another sweet onion variety. Regular yellow onions will work but won’t have that natural candy-like sweetness that makes this casserole special.
• Saute the onions until they’re soft and translucent but not caramelized. You want them tender, not browned.
• Assemble the casserole in the morning and refrigerate. It’s ready to pop in the oven before dinner with no last-minute prep.

Variations

• Use Gruyere instead of Swiss for a nuttier, more complex cheese flavor.
• Add a layer of sliced ham between the onions and bread for a heartier main dish.
• Swap French bread for sourdough for a tangier bread layer.